View Single Post
Old 06-21-2013, 09:40 PM   #20 (permalink)
Freebase Dali
Partying on the inside
Freebase Dali's Avatar
Join Date: Mar 2009
Posts: 5,329

I just want to post something here for those of you that do your own recording, as it seems to be a pretty big factor that man people recording digitally don't take into account:

Recording levels.
What I mean by this is no matter what digital recording equipment you have, whether it's miked acoustic instruments into an audio interface and into recording software, or a standalone digital recorder, and no matter how low or high budget that setup is, your first and foremost concern when recording digitally should be your gain.

Back in the day when everything was recorded in the analog domain, you could get away with recording too hot. In fact, it created quite a nice effect that people still use today, and many digital plugins try to emulate. But when it comes to recording in the digital domain, digital distortion is definitely not a good thing. Sure, overdriving sounds great on tubes and tape, but in the digital world, when you go over a certain point, you will simply create a nasty, distracting effect.

So what am I talking about here?
Ok. Let's say you're an acoustic guitarist. You have a cheap microphone and a cheap audio interface and you're just recording to one track in a cheap music program. While your thoughts may be primarily on the cheapness of your mic, interface and music program, THE BEST THING YOU CAN DO FOR YOUR RECORDINGS is to just ensure that when you record, your levels are not going over 0 decibels. In fact, I would recommend that they don't go over -6 decibels at the very loudest parts, assuming you're recording in 24 bits. (Which you should be)

So how do we know whether we're going over 0 db or not? First let's talk about gain staging, and bring level metering into it.

Gain staging is ensuring the proper and optimal gain for your signal throughout all gain-influential points in the signal path. This is typically from your instrument > amplifier/preamp > amp/preamp output > input gain on your mixer and/or interface > output level on the interface, then finally, the input gain on the track that you are recording into in your program. Additionally, if you use plugins in your program that affect the signal before recording, each subsequent plugin in serial has an input/output gain stage. (This is true after recording as well, however it's adjustable after the fact)

So, if you understand that each of these points in the chain can affect the signal level, then you should understand that you need to control the level at each of these points where necessary, starting from the instrument and going forward all the way to the input gain of your recording device or track.
We use level meters to determine how hot our signal is throughout the chain. Sometimes you may only be limited to a level meter on your interface, and on your recording track and master channel. That's fine. You can start off in a great position by utilizing the unity gain concept.

Unity Gain
This is the concept of not changing the level of the signal through each point in the path. On mixers, this point is usually represented by a U. (Unity)
On some other devices, it may just be a tactile notch that you feel when the dial is up the middle.
Basically this is just leaving the signal the same, without lowering it or raising it. This is important to know, because when we know that we are not processing a signal that would add more or less level to the signal, then we are not unnecessarily changing the signal level, especially if it ends up with us overdriving along the signal chain and introducing digital distortion that we cannot get rid of in the recording.

For instance:
You have a guitar going through a multi-FX pedal which is DI'd into an instrument input on your audio interface, which sends to a recording track in your music program. Let's say you have your guitar wide open (which would be fine), your pedal input set to whatever sounds good, then you jack up the pedal output to 11 and send that whole signal to your interface, which has its input level set to 11, and its output set to 11...
(I use 11, because there usually isn't an 11. Which would definitely be way too high)
Then in your program you have everything at unity gain. Input is at 0 and track volume at 0.
Do you think your signal will be at unity gain?
No sir.
You will likely be overdriven on the recording track. And when you hit the record button, the negative effects of digital distortion are there to stay. The only way to undo it is to record all over again with the proper levels leading up to that point.
Even if you overdrive up to your recording track then lower the gain into your recording track, if you have digitally overdriven something ahead of it, the effect may still be there. That is why gain staging is important when dealing in the digital realm.

Using the peak meters on your gear is a good way to tell if you're overdriving. Most audio interfaces will have this, even if in the form of a software mixer that comes with it that lets you see the levels bouncing up and down. Try to use them as close to the source as possible to get your acceptable level, then work your way forward.

I would recommend that if your first meter is at your audio interface, that you set your instrument how you want it, set your microphone how you want it, then set your mixer or interface input gain based on the meters. Go up or down so that you're sitting no higher than -6 db on your loudest parts. -12 db on average is fine. It's probably a 24 bit device, so we don't have to worry about the noise floor issues we had when we could only record with 16 bits of headroom.
Once you have the input gain set on the mixer or interface, unity gain EVERYTHING past that. You will know that you have succeeded at unity gain past the input of your interface or mixer ahead of your recording track when you monitor the recording track in your program and look at where its meter is peaking. If it's the same as the mixer or interface, you're good. Stay at that level. Do not be tempted to turn up gains so you can hear yourself better. Use monitor volumes to do that, as they will not affect your input gains.
If your recording track is peaking a lot higher than the meter behind it, something in between those meters needs to be lowered. Lower the first output gain after the first meter, then work your way forward. Your goal is to have your desired first signal be equal all the way through. This way, you will have the best representation of your signal while preventing stages from putting that signal over the limit.

Finally, it's important to know that when dealing with digital hardware and software, there may be situations where you don't hear the negative effects of digital overdriving if they operate in higher bitrates during the processing phase. (Music programs will usually operate in at least 32 bits!) You will typically hear the effects when hitting converters that operate in a lower bit rate, and exporting/converting from your project to lower bitrates to support the 16 bit standard we use with Wav and MP3.
This is because there is temporary "headroom" there, since the bits are available at the time. However, if we don't account for the fact that, at some point, the bits will not be available, we will ultimately end up with the conversion simply chopping off the signal where it exceeds the limit, and introducing some very nasty sounding effects.
This is an important concept in the mixing phase when you've recorded your instruments all nice and clean and at the proper levels, then begin to add more elements without compensating for the additive effect that all those elements have when they sum to the final stereo bus.
This is very typical due to a lack of understanding that gain staging continues even into the stage after you have recorded and have begun to process the signal or have added more recordings along side. In this case, hope is not lost if we have properly maintained a reasonable level for each individual recording or element. Assuming we did, we can then bring down the levels of each element so that, at the master channel, the totality of the signal is not going above 0 db.

So, I hope this has helped someone.
Ensuring proper levels is not the only step, but it's an important one, because you can have the best digital equipment in the world, but if you violate the 0 db rule, not a single person in the world can fix the issue after the fact. So please do pay mind. You can always raise levels after. You can't remove digital distortion after. It's just part of the recording.
Freebase Dali is offline   Reply With Quote